Effect of rare earth additives on properties of silicon nitride ceramics

Abstract

Silicon nitride ceramics with rare earth (Re) compound (5 wt-%) and MgO (3 wt-%) additives were fabricated by spark plasma sintering and following heat treatment. The Re compounds included two groups: ReF₃ ((Re = La,Nd,Gd) and Re₂O₃ (Re = La,Nd,Gd). Specimens show the same tendency in the sintering shrinkage rate, relative density, grain size and bending strength with the increasing Re cation (Re³⁺) radius both in ReF₃ and Re₂O₃ added samples. However, as to aspect ratios and thermal conductivity, the change rules are completely opposite between the two groups of specimens.

Keywords:

• Silicon nitride ceramics
• Thermal conductivity
• Rare earth oxide
• Rare earth fluoride

Acknowledgements

This work was supported by the National Science Foundation under grant no. 51272122.